1. Field of the Invention
The present invention relates to a power semiconductor device and a method of fabricating the same.
2. Description of the Related Art
An insulated gate bipolar transistor (IGBT) is a transistor having a gate fabricated using metal oxide semiconductor (MOS) and having bipolarity by forming a p-type collector layer on a rear surface thereof.
Since a power metal oxide semiconductor field effect transistor (MOSFET) has been developed, the MOSFET has been used in a region requiring high-speed switching characteristics.
However, since the MOSFET has structural limitations, a bipolar transistor, a thyristor, gate turn-off thyristors (GTOs), and the like, have been used in regions requiring high voltage.
The IGBT has characteristics such as a low forward loss and high-speed switching, and therefore has been expanded into fields that cannot be realized by the existing thyristor, bipolar transistor, metal oxide semiconductor field effect transistor (MOSFET), and the like.
Reviewing an operational principle of the IGBT, when the IGBT device is turned on, an amount of voltage higher than that applied to a cathode is applied to an anode and an amount of voltage higher than the threshold voltage of the device is applied to a gate electrode, such that a polarity of a surface of a p-type body region located in a lower portion of the gate electrode is reversed, thereby forming an n-type channel.
Electronic current injected into a drift region through a channel induces the injection of hole current from a high-concentration p-type collector layer located in a lower portion of the IGBT device, like a base current of the bipolar transistor.
Due to the high-concentration injection of minority carriers, conductivity modulation, by which conductivity in the drift region is increased tens to hundreds of times, occurs.
Unlike the MOSFET, a resistance component in the drift region is very low due to the conductivity modulation, such that the IGBT may have very high voltages applied thereto.
Current flowing in the cathode is divided into electronic current flowing through a channel and hole current flowing through a junction between the p-type body and the n-type drift region.
The IGBT has a pnp structure between the anode and the cathode in terms of the substrate structure and does not have a diode embedded therein, unlike the MOSFET, such that separate diodes need to be connected to each other in an antiparallel manner.
The IGBT has main characteristics, such as the maintenance of blocking voltage, the reduction in a conduction loss, and the increase in a switching speed.
In the related art, the magnitude in voltage required for the IGBT tends to be increased, and the durability of the device needs to be increased accordingly.
However, as the device is miniaturized, a latch-up occurs due to the device structure when the magnitude in voltage is increased, such that the device may be easily broken.
The latch-up means that when a pnpn parasitic thyristor structurally present in the IGBT is operated, the IGBT may no longer be controlled by a gate, and thus a large amount of current flows to the IGBT to overheat and break the device.
In addition, as the device is miniaturized, a short circuit occurs in the IGBT.
The short circuit, which mainly occurs in the case of a load connected to the device, for example, an inductive load such as a motor, means the case in which the gate is applied with current in the state in which high voltage is applied to the IGBT and thus high voltage and large current are simultaneously applied to the IGBT.
A short circuit immunity of the IGBT is evaluated as the time for which the device is kept in the foregoing short circuit state without being broken.
Therefore, in order to secure miniaturization and reliability of the IGBT, a need exists for a method for securing robustness for the latch-up and increasing short circuit immunity.
The following related art document discloses the invention relating to an insulated gate bipolar transistor (IGBT).
However, the invention of the following related art document does not include a segregation stop layer formed on a surface of a gate oxide film like the present invention, and does not disclose a structure for increasing a channel length formed on a surface of a gate when a device is turned on, and therefore is different from the present invention.